Antireflective glass substrate and method for manufacturing the same

ABSTRACT

A method for manufacturing antireflective glass substrates by ion implantation, comprising selecting a source gas of N2, or O2, ionizing the source gas so as to form a mixture of single charge and multicharge ions of N, or O, forming a beam of single charge and multicharge ions of N, or O by accelerating with an acceleration voltage A between 13 kV and 40 kV and setting the ion dosage at a value between 5.56×1014×A/kV+4.78×1016 ions/cm2 and −2.22×1016×A/kV+1.09×1018 ions/cm2, as well as antireflective glass substrates comprising an area treated by ion implantation with a mixture of simple charge and multicharge ions according to this method.

The present invention relates to an antireflective glass substrate and a method of manufacturing the same. It also relates to the use of an antireflective glass substrate, particularly as glazing.

Most antireflective glass substrates are obtained by the deposition of coatings on the glass surface. Reduction of light reflectance is obtained by single layers having refractive indexes that are lower than the refractive index of the glass substrate or that have a refractive index gradient. High performance antireflective glass substrates are obtained by stacks of multiple layers that make use of interference effects in order to obtain a significant reduction of light reflectance over the whole visible range. Such high performance antireflective layer stacks, applied to both sides of the substrate, are able to reduce the light reflectance of a typical glass substrate from about 8% to 4% or even less. However they require multiple layer deposition steps with elaborate composition control and layer thickness control, making it a difficult and thus expensive process. Furthermore single antireflective layers and in particular multiple layer stacks, usually deposited by physical vapor deposition, are more sensitive to mechanical and/or chemical attack than the glass itself.

Another antireflective glass substrate has been disclosed in FR1300336. Here an antireflection effect is obtained by implanting heavy ions of noble gases at a concentration of 10 atomic % up to depths of 100 nm or 200 nm into the surface of a glass substrate. However noble gases are relatively expensive and the need to reach such high concentrations of the implanted noble gas ions in the glass substrate increases the risk of creating important damage to the glass network.

There is therefore a need in the art to provide a simple, inexpensive method of making an antireflective glass substrate.

According to one of its aspects, the subject of the present invention is to provide a method for producing an antireflective glass substrate.

According to another of its aspects, the subject of the present invention is to provide an antireflective glass substrate.

The invention relates to a method for producing an antireflective glass substrate comprising the following operations:

-   -   providing a source gas selected from O₂ and/or N₂,     -   ionizing the source gas so as to form a mixture of single charge         ions and multicharge ions of O and/or N,     -   accelerating the mixture of single charge ions and multicharge         ions of O and/or N with an acceleration voltage so as to form a         beam of single charge ions and multicharge ions of O and/or N         wherein the acceleration voltage A is comprised between 13 kV         and 40 kV and the ion dosage D is comprised between         5.56×10¹⁴×A/kV+4.78×10¹⁶ ions/cm² and −2.22×10¹⁶×A/kV+1.09×10¹⁸         ions/cm²,     -   providing a glass substrate,     -   positioning the glass substrate in the trajectory of the beam of         single charge and multicharge ions of O and/or N.

The inventors have surprisingly found that the method of the present invention providing an ion beam comprising a mixture of single charge and multicharge ions of O and/or N, accelerated with the same specific acceleration voltage and at such specific dosage, applied to a glass substrate, leads to a reduced reflectance. Advantageously the reflectance of the resulting glass substrate is decreased from about 8% to at most 6.5%, preferably at most 6%, more preferably at most 5.5%. Most surprisingly this low level of reflectance is reached whereas the concentration of implanted N, for example, is below 2 atomic % throughout the implanted depth and furthermore it was expected initially that the implantation of nitrogen would lead to silicon-nitrogen bonds, creating silicon oxynitride-comprising material layers having higher refractive index than the untreated glass substrate.

According to the present invention the source gas, chosen from O₂ and/or N₂, is ionized so as to form a mixture of single charge ions and multicharge ions of O and/or N. The beam of accelerated single charge ions and multicharge ions may comprise various amounts of the different O and/or N ions. Example currents of the respective ions are shown in Table 1 below (measured in milli Ampere).

TABLE 1 Ions of O Ions of N O⁺ 1.35 mA N⁺ 0.55 mA O²⁺ 0.15 mA N²⁺ 0.60 mA N³⁺ 0.24 mA

For a given ion type, the key ion implantation parameters are the ion acceleration voltage, and the ion dosage.

The positioning of the glass substrate in the trajectory of the beam of single charge and multicharge ions is chosen such that certain amount of ions per surface area or ion dosage is obtained. The ion dosage, or dosage is expressed as number of ions per square centimeter. For the purpose of the present invention the ion dosage is the total dosage of single charge ions and multicharge ions. The ion beam preferably provides a continuous stream of single and multicharge ions. The ion dosage is controlled by controlling the exposure time of the substrate to the ion beam. According to the present invention multicharge ions are ions carrying more than one positive charge. Single charge ions are ions carrying a single positive charge.

In one embodiment of the invention the positioning comprises moving glass substrate and ion implantation beam relative to each other so as to progressively treat a certain surface area of the glass substrate. Preferably they are moved relative to each other at a speed comprised between 0.1 mm/s and 1000 mm/s. The speed of the movement of the glass relative to the ion implantation beam is chosen in an appropriate way to control the residence time of the sample in the beam which influences ion dosage of the area being treated.

The method of the present invention can be easily scaled up so as to treat large substrates of more than 1 m², for example by continuously scanning the substrate surface with an ion beam of the present invention or for example by forming an array of multiple ion sources that treat a moving substrate over its whole width in a single pass or in multiple passes.

According to the present invention the acceleration voltage and ion dosage are preferably comprised in the following ranges:

TABLE 2 parameter Acceleration voltage A [kV] Ion dosage D [ions/cm²] general range 13 to 40 5.56 × 10¹⁴ × A/kV + 4.78 × 10¹⁶ to −2.22 × 10¹⁶ × A/kV + 1.09 × 10¹⁸ preferred range 15 to 35 7.50 × 10¹⁴ × A/kV + 4.88 × 10¹⁶ to −2.05 × 10¹⁶ × A/kV + 8.08 × 10¹⁷ most preferred 16 to 25 1.11 × 10¹⁵ × A/kV + 4.72 × 10¹⁶ range to −2.78 × 10¹⁶ × A/kV + 7.94 × 10¹⁷

The inventors have found that ion sources providing an ion beam comprising a mixture of single charge and multicharge ions, accelerated with the same acceleration voltage are particularly useful as they may provide lower dosages of multicharge ions than of single charge ions. It appears that a glass substrate having a low reflectance layer may be obtained with the mixture of single charge ions, having higher dosage and lower implantation energy, and multicharge ions, having lower dosage and higher implantation energy, provided in such a beam. The implantation energy, expressed in Electron Volt (eV) is calculated by multiplying the charge of the single charge ion or multicharge ion with the acceleration voltage.

In a preferred embodiment of the present invention the temperature of the area of the glass substrate being treated, situated under the area being treated is less than or equal to the glass transition temperature of the glass substrate. This temperature is for example influenced by the ion current of the beam, by the residence time of the treated area in the beam and by any cooling means of the substrate.

In a preferred embodiment of the invention implanted ions of either N or O are used. In another embodiment of the invention implanted ions of N and O are combined. These alternatives are covered herein by the wording “and/or”.

In one embodiment of the invention several ion implantation beams are used simultaneously or consecutively to treat the glass substrate.

In one embodiment of the invention the total dosage of ions per surface unit of an area of the glass substrate is obtained by a single treatment by an ion implantation beam.

In another embodiment of the invention the total dosage of ions per surface unit of an area of the glass substrate is obtained by several consecutive treatments by one or more ion implantation beams.

The method of the present invention is preferably performed in a vacuum chamber at a pressure comprised between 10⁻² mbar and 10⁻⁷ mbar, more preferably at between 10⁻⁵ mbar and 10⁻⁶ mbar.

An example ion source for carrying out the method of the present invention is the Hardion+ RCE ion source from Quertech Ingénierie S.A.

The light reflectance is measured in the visible light range on the side of the substrate treated with the ion implantation method of the present invention using illuminant D65, 2°.

The present invention also concerns the use of a mixture of single charge and multicharge ions of N and/or O to decrease the reflectance of a glass substrate, the mixture of single charge and multicharge ions being implanted in the glass substrate with an ion dosage and acceleration voltage effective to reduce the reflectance of the glass substrate.

Advantageously the mixture of single and multicharge ions of O and/or N is used with an ion dosage and acceleration voltage effective to reduce the reflectance of a glass substrate to at most 6.5%, preferably to at most 6%, more preferably to at most 5.5%.

According to the present invention, the mixture of single charge and multicharge ions of O and/or N preferably comprises, O⁺ and O²⁺ and/or N⁺, N²⁺ and N³⁺ respectively.

According to a preferred embodiment of the present invention, mixture of single charge and multicharge ions of O comprises a lesser amount of O²⁺ than of O⁺. In a more preferred embodiment of the present invention the mixture of single charge and multicharge ions of O comprises 55-98% of O⁺ and, 2-45% of O²⁺.

According to another preferred embodiment of the present invention, mixture of single charge and multicharge ions of N comprises a lesser amount of N³⁺ than of N⁺ and of N²⁺ each. In a more preferred embodiment of the present invention the mixture of single charge and multicharge ions of N comprises 40-70% of N⁺, 20-40% of N²⁺, and 2-20% of N³⁺.

According to the present invention the acceleration voltage and ion dosage effective to reduce reflectance of the glass substrate are preferably comprised in the following ranges:

TABLE 3 parameter Acceleration voltage A [kV] Ion dosage D [ions/cm²] general range 13 to 40 5.56 × 10¹⁴ × A/kV + 4.78 × 10¹⁶ to −2.22 × 10¹⁶ × A/kV + 1.09 × 10¹⁸ preferred range 15 to 35 7.50 × 10¹⁴ × A/kV + 4.88 × 10¹⁶ to −2.05 × 10¹⁶ × A/kV + 8.08 × 10¹⁷ most preferred 16 to 25 1.11 × 10¹⁵ × A/kV + 4.72 × 10¹⁶ range to −2.78 × 10¹⁶ × A/kV + 7.94 × 10¹⁷

The present invention also concerns an ion implanted glass substrate having reduced reflectance, wherein the ions are single charge and multicharge ions of N and/or O.

Advantageously the ion implanted glass substrates of the present invention, have a reflectance of at most 6.5%, preferably at most 6% more preferably at most 5.5%. The reflectance is measured on the treated side with D65 illuminant and a 2° observer angle.

The reflectance is measured on the treated side with D65 illuminant and a 2° observer angle. The scratch resistance is measured on the treated side as described below.

In a preferred embodiment of the present invention the ions implanted in the glass substrates of the present invention are single charge and multicharge ions of N.

Advantageously the implantation depth of the ions may be comprised between 0.1 μm and 1 μm, preferably between 0.1 μm and 0.5 μm.

The glass substrate used in the present invention is usually a sheet like glass substrate having two opposing major surfaces. The ion implantation of the present invention may be performed on one or both of these surfaces. The ion implantation of the present invention may be performed on part of a surface or on the complete surface of the glass substrate.

In another embodiment, the present invention also concerns glazings incorporating glass substrates of the present invention, no matter whether they are monolithic, laminated or multiple with interposed gas layers. In such embodiment, the substrate may be tinted, tempered, reinforced, bent, folded or ultraviolet filtering.

These glazings can be used both as internal and external building glazings, and as protective glass for objects such as panels, display windows, glass furniture such as a counter, a refrigerated display case, etc., also as automotive glazings such as laminated windshields, mirrors, antiglare screens for computers, displays and decorative glass.

The glazing incorporating the glass substrate according to the invention may have interesting additional properties. Thus, it can be a glazing having a security function, such as the laminated glazings. It can also be a glazing having a burglar proof, sound proofing, fire protection or anti-bacterial function.

The glazing can also be chosen in such a way that the substrate treated on one of its faces with the method according to the present invention, comprises a layer stack deposited on the other of its faces. The stack of layers may have a specific function, e.g., sun-shielding or heat-absorbing, or also having an anti-ultraviolet, antistatic (such as slightly conductive, doped metallic oxide layer) and low-emissive, such as silver-based layers of the or doped tin oxide layers. It can also be a layer having anti-soiling properties such as a very fine TiO₂ layer, or a hydrophobic organic layer with a water-repellent function or hydrophilic layer with an anti-condensation function.

The layer stack can be a silver comprising coating having a mirror function and all configurations are possible. Thus, in the case of a monolithic glazing with a mirror function, it is of interest to position an antireflective glass substrate of the present invention with the treated face as face 1 (i.e., on the side where the spectator is positioned) and the silver coating on face 2 (i.e., on the side where the mirror is attached to a wall), the antireflective face 1 according to the invention thus preventing the splitting of the reflected image.

In the case of a double glazing (where according to convention the faces of glass substrates are numbered starting with the outermost face), it is thus possible to use the antireflective treated face as face 1 and the other functional layers on face 2 for anti-ultraviolet or sun-shielding and 3 for low-emissive layers. In a double glazing, it is thus possible to have at least one antireflection stack on one of the faces of the substrates and at least one layer or a stack of layers providing a supplementary functionality. The double glazing can also have several antireflective treated faces, particularly at least on faces 2, 3, or 4.

The substrate may also undergo a surface treatment, particularly acid etching (frosting). The ion implantation treatment may be performed on the etched face or on the opposite face.

The substrate, or one of those with which it is associated, can also be of the printed, decorative glass type or can be screen process printed.

A particularly interesting glazing incorporating the antireflective glass substrate according to the invention is a glazing having a laminated structure with two glass substrates, comprising a polymer type assembly sheet between an antireflective glass substrate of the present invention, with the ion implantation treated surface facing away from the polymer assembly sheet, and another glass substrate. The polymer assembly sheet can be from polyvinylbutyral (PVB) type, polyvinyl acetate (EVA) type or polycyclohexane (COP) type.

This configuration, particularly with two heat treated, that is bent and/or tempered, substrates, makes it possible to obtain a car glazing and in particular a windshield. The standards require cars to have windshields with a high light transmission of at least 75% in normal incidence. Due to the incorporation of the heat treated antireflective glass substrate in a laminated structure of a conventional windshield, the light transmission of the glazing is particularly improved, so that its energy transmission can be slightly reduced by other means, while still remaining within the light transmission standards. Thus, the sun-shielding effect of the windshield can be improved, e.g., by absorption of the glass substrates. The light reflection value of a standard, laminated windshield can be brought from 8% to less than 5%.

The glass substrate according to this invention may be a glass sheet of any thickness having the following composition ranges expressed as weight percentage of the total weight of the glass:

SiO₂ 35-85%,  Al₂O₃ 0-30%, P₂O₅ 0-20%, B₂O₃ 0-20%, Na₂O 0-25%, CaO 0-20%, MgO 0-20%, K₂O 0-20%, and BaO 0-20%.

The glass substrate according to this invention is preferably a glass sheet chosen among a soda-lime glass sheet, a borosilicate glass sheet, or an aluminosilicate glass sheet.

The glass substrate according to this invention preferably bears no coating on the side being subjected to ion implantation.

The glass substrate according to the present invention may be a large glass sheet that will be cut to its final dimension after the ion implantation treatment or it may be a glass sheet already cut to its final size.

Advantageously the glass substrate of the present invention may be a float glass substrate. The ion implantation method of the present invention may be performed on the air side of a float glass substrate and/or the tin side of a float glass substrate. Preferably the ion implantation method of the present invention is performed on the air side of a float glass substrate.

In an embodiment of the present invention the glass substrate may be a previously chemically strengthened glass substrate.

The optical properties were measured using a Hunterlab Ultrascan Pro Spectrophotometer.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

The ion implantation examples were prepared according to the various parameters detailed in the tables below using an RCE ion source for generating a beam of single charge and multicharge ions. The ion source used was a Hardion+ RCE ion source from Quertech Ingénierie S.A.

All samples had a size of 10×10 cm² and were treated on the entire surface by displacing the glass substrate through the ion beam at a speed between 20 and 30 mm/s.

The temperature of the area of the glass substrate being treated was kept at a temperature less than or equal to the glass transition temperature of the glass substrate.

For all examples the implantation was performed in a vacuum chamber at a pressure of 10⁻⁶ mbar.

Using the RCE ion source, ions of N or O were implanted in 4 mm thick regular clear soda-lime glass and alumino-silicate glass substrates. Before being implanted with the ion implantation method of the present invention the reflectance of the glass substrates was about 8%. The key implantation parameters, and measured reflectance measurements can be found in the tables below.

TABLE 4 acceler- ation Light refer- Source glass voltage ion dosage reflectance ence gas substrate [kV] [ions/cm²] [%, D65, 2°] E1 N₂ Sodalime 35 7 × 10¹⁶ 6.5 E2 N₂ Sodalime 35 2.5 × 10¹⁷  6.45 E3 N₂ Sodalime 35 1 × 10¹⁷ 6.37 E4 N₂ Sodalime 20 5 × 10¹⁷ 6.25 E5 N₂ Sodalime 15 7.5 × 10¹⁷  6.23 E6 N₂ Sodalime 20 6 × 10¹⁶ 6.14 E7 N₂ Sodalime 25 7 × 10¹⁶ 6 E8 N₂ Sodalime 20 6.5 × 10¹⁶  5.98 E9 N₂ Sodalime 35 7.5 × 10¹⁶  5.96 E10 N₂ Sodalime 25 2.5 × 10¹⁷  5.76 E11 N₂ Sodalime 20 7 × 10¹⁶ 5.47 E12 N₂ Sodalime 25 7.5 × 10¹⁶  5.25 E13 N₂ Sodalime 25 9 × 10¹⁶ 5.15 E14 N₂ Sodalime 25 8 × 10¹⁶ 5.05 E15 N₂ Sodalime 20 9 × 10¹⁶ 4.99 E16 N₂ Aluminosilicate 25 8 × 10¹⁶ 5.87 E17 N₂ Aluminosilicate 25 7 × 10¹⁶ 5.67 E18 N₂ Aluminosilicate 20 7 × 10¹⁶ 5.35 E19 N₂ Aluminosilicate 20 8 × 10¹⁶ 5.13 E20 N₂ Aluminosilicate 25 9 × 10¹⁶ 4.93 E21 N₂ Aluminosilicate 20 9 × 10¹⁶ 4.66 C1 N₂ Sodalime 25 7.5 × 10¹⁷  7.75 C2 N₂ Sodalime 35 6 × 10¹⁶ 6.92 C3 N₂ Sodalime 25 6 × 10¹⁶ 6.50 C4 N₂ Aluminosilicate 35 6 × 10¹⁶ 7.02

As can be seen on examples E1 to E15, according to the present invention, treatment of the sodalime glass samples with an ion beam comprising a mixture of single charge and multicharge ions of N, accelerated with the same specific acceleration voltage and at such specific dosage, applied to a glass substrate, leads to a reduced reflectance of not more than 6.5%. Comparative sodalime examples C1 to C3 lead to reduced reflectance but the acceleration voltage and ion dosage of these examples is not appropriate to reduce the reflectance to 6.5% or less.

As can be seen on examples E16 to E21, according to the present invention, treatment of the aluminosilicate glass samples with an ion beam comprising a mixture of single charge and multicharge ions of N, accelerated with the same specific acceleration voltage and at such specific dosage, applied to a glass substrate, lead to a reduced reflectance of not more than 6.5%. Comparative aluminosilicate example C4 leads to reduced reflectance but the acceleration voltage and ion dosage of these examples is not appropriate to reduce the reflectance to 6.5% or less.

As can be seen on examples E7 to E15, according to the present invention, treatment of the sodalime glass samples with an ion beam comprising a mixture of single charge and multicharge ions of N, accelerated with the same specific acceleration voltage and at such specific dosage, applied to a glass substrate, lead to a reduced reflectance of not more than 6%.

As can be seen on examples E11 to E15, according to the present invention, treatment of the sodalime glass samples with an ion beam comprising a mixture of single charge and multicharge ions of N, accelerated with the same specific acceleration voltage and at such specific dosage, applied to a glass substrate, lead to a reduced reflectance of not more than 5.5%.

Furthermore XPS measurements were made on the samples E1 to E21 of the present invention and it was found that the atomic concentration of implanted ions of N is below 8 atomic % throughout the implantation depth. 

The invention claimed is:
 1. A method for producing an antireflective glass substrate comprising: a) providing a source gas selected from O₂ and/or N₂, b) ionizing the source gas so as to form a mixture of single charge ions and multicharge ions of O and/or N, c) accelerating the mixture of single charge ions and multicharge ions of O and/or N with an acceleration voltage so as to form a beam of single charge ions and multicharge ions of O and/or N wherein an acceleration voltage A is between 13 kV and 40 kV and an ion dosage D is between 5.56×10¹⁴×A/kV+4.78×10¹⁶ ions/cm² and −2.22×10¹⁶×A/kV+1.09×10¹⁸ ions/cm², d) providing a glass substrate, e) positioning the glass substrate in a trajectory of the beam of single charge and multicharge ions of O and/or N, and f) implanting the single charge and multicharge ions of O and/or N such that a concentration of implanted O and/or N is below 2 atomic % throughout an implanted depth in the glass substrate.
 2. The method for producing an antireflective glass substrate according to claim 1, wherein the acceleration voltage is between 15 kV and 35 kV and the ion dosage D is between 7.50×10¹⁴×A/kV+4.88×10¹⁶ ions/cm² and −2.05×10¹⁶×A/kV+8.08×10¹⁷ ions/cm².
 3. The method for producing an antireflective glass substrate according to claim 2, wherein the acceleration voltage is between 16 kV and 25 kV and the ion dosage is between 1.11×10¹⁵×A/kV+4.72×10¹⁶ ions/cm² and −2.78×10¹⁶×A/kV+7.94×10¹⁷ ions/cm².
 4. The method for producing an antireflective glass substrate according to claim 1, wherein the glass substrate provided has the following composition ranges expressed as weight percentage of the total weight of the glass: SiO₂ 35-85%,  Al₂O₃ 0-30%, P₂O₅ 0-20%, B₂O₃ 0-20%, Na₂O 0-25%, CaO 0-20%, MgO 0-20%, K₂O 0-20%, and BaO 0-20%.


5. A method for producing a color antireflective glass substrate according to claim 4, wherein the glass substrate is selected from a soda-lime glass sheet, a borosilicate glass sheet or an aluminosilicate glass sheet.
 6. A method for decreasing a reflectance of a glass substrate, comprising: implanting a mixture of single charge and multicharge ions of N and/or O in the glass substrate with an ion dosage and acceleration voltage effective to reduce the reflectance of the glass substrate, wherein the implanting of single charge and multicharge ions of O and/or N result in a concentration of implanted O and/or N is below 2 atomic % throughout an implanted depth in the glass substrate.
 7. The method for decreasing the reflectance of a glass substrate according to claim 6, wherein the implanting is effective to reduce the reflectance of the glass substrate to at most 6.5%.
 8. The method for decreasing the reflectance of a glass substrate according to claim 7, wherein the implanting is effective to reduce the reflectance of the glass substrate to at most 6%.
 9. The method for decreasing the reflectance of a glass substrate according to claim 8, wherein the implanting is effective to reduce the reflectance of the glass substrate to at most 5.5%.
 10. The method for decreasing the reflectance of a glass substrate according to claim 6, wherein during the implanting the mixture of single charge and multicharge ions being implanted in the glass substrate has an acceleration voltage A between 13 kV and 40 kV and an ion dosage D between 5.56×10¹⁴×A/kV+4.78×10¹⁶ ions/cm² and −2.22×10¹⁶×A/kV+1.09×10¹⁸ ions/cm².
 11. The method for producing an antireflective glass substrate according to claim 1, wherein the source gas comprises O₂.
 12. The method for producing an antireflective glass substrate according to claim 1, wherein the source gas comprises N₂.
 13. A method for producing an antireflective glass substrate comprising: a) providing a source gas selected from O₂ and/or N₂, b) ionizing the source gas so as to form a mixture of single charge ions and multicharge ions of O and/or N, c) accelerating the mixture of single charge ions and multicharge ions of O and/or N with an acceleration voltage so as to form a beam of single charge ions and multicharge ions of O and/or N wherein an acceleration voltage A is between 13 kV and 40 kV and an ion dosage D is between 5.56×10¹⁴×A/kV+4.78×10¹⁶ ions/cm² and −2.22×10¹⁶×A/kV+1.09×10¹⁸ ions/cm², d) providing a glass substrate, and e) positioning the glass substrate in a trajectory of the beam of single charge and multicharge ions of O and/or N, f) implanting a mixture of single charge and multicharge ions of N and/or O in the glass substrate with an ion dosage and acceleration voltage effective to reduce the reflectance of the glass substrate, wherein the implanting is effective to reduce the reflectance of the glass substrate to at most 5.5%.
 14. The method for producing an antireflective glass substrate according to claim 13, further comprising displacing the glass substrate through the ion beam at a speed of between 20 and 30 mm/s. 